Television display devices for use in the United States with screen size of 13 inches or greater are required to decode and display closed caption messages. This requirement specifies a common set of character-based display capabilities including the number of rows, columns, colors and a basic character-set that provides an on screen display or OSD capability. In addition such on screen display capability can facilitate the display of user controls, for example, channel selection, audio and video setting and maintenance adjustments. On screen messages are generated by a microcontroller from a stored character set and are inserted into the R, G and B video signals coupled for display.
On occasions, maintenance or diagnosis of problems within TV or video display device can necessitate the use of an oscilloscope or logic analyzer to determine the presence and qualitative characteristics of certain waveforms. For example, an infra red or IR remote signal originating from a hand-held remote-control unit is typically detected within a display device by circuitry sensitive to the particular characteristics such as, optical wavelength, modulation frequency, etc. of that signal. The detected, or often termed the envelope signal is coupled to other functional systems within the display device as a serial digital signal. These other systems typically decode signal and reconstruct the intended remote-control command which is then executed yielding the desired response. However, a remote control unit can generate an encoded control signal unknown to the display device, particularly, for example, when a third-party set-top box receives a detected-IR signal from the display device to which it is connected, decodes the signal and initiates appropriate action itself. In either arrangement, when the anticipated command is not executed, it can be useful to monitor the intermediate, or decoded signal to assess whether or not it represents the general signal pattern expected in response to a button-press on the remote control. In this way the problem can be isolated to points preceding or succeeding the signal monitoring point.
Furthermore, within a display device various functional-blocks communicate between themselves at periodic intervals via serial communication busses, and many of such functional blocks employ internal feedback signals as part of control loops. Clearly a simple, cost effective monitoring arrangement is required to indicate received control signal sequences or diagnose the general electronic well-being of the video display device.